Sexual abuse in the ultra-Orthodox Jewish community has long been hidden. Victims who came forward were intimidated into silence; their families were shunned; cases were dropped for a lack of cooperation.

But on Monday, a State Supreme Court jury in Brooklyn delivered a stunning victory to prosecutors and victims’ advocates, convicting a 54-year-old unlicensed therapist who is a prominent member of the Satmar Hasidic community of Williamsburg of repeatedly sexually abusing a young girl who had been sent to him for help.

“The veil of secrecy has been lifted,” said Charles J. Hynes, the Brooklyn district attorney. “The wall that has existed in parts of these communities has now been broken through. And as far as I’m concerned, it is very clear to me that it is only going to get better for people who are victimized in these various communities.”

The case against the therapist, Nechemya Weberman, was a significant milestone for Mr. Hynes, whose office has been criticized for not acting aggressively enough against sexual abusers in the borough’s large and politically connected ultra-Orthodox community.

The verdict represented the first time Mr. Hynes’ office has won a conviction of a prominent member of the Satmar Hasidic community of Williamsburg for child sexual abuse.

The case also offered a glimpse of the Satmar community’s shadowy efforts to enforce rigid codes of behavior — particularly for young girls — by allowing so-called modesty committees to intimidate girls for wearing revealing clothing or using cellphones, and requiring parents to send children judged to be breaking rules to religious counselors, many of whom are not licensed and charge high fees.

The trial of Mr. Weberman, which began on Nov. 26, was a difficult one because there was no physical evidence; the trial hinged on the credibility of Mr. Weberman, who is well connected and powerful in his community, and that of a young woman who had been shunned for being a rebellious teen. The girl said Mr. Weberman had abused her for three years, starting when she was 12, groping her and forcing her to perform oral sex. He denied he had ever touched her.

The jury believed the young woman and convicted Mr. Weberman of all 59 counts against him. Justice John G. Ingram scheduled a sentencing on Jan. 9; the most serious charge carries a maximum sentence of 25 years, but depending on how the sentence is structured, Mr. Weberman could spend even longer in prison.

Samuel Heilman, a professor of sociology at Queens College of the City University of New York who studies the Hasidic community, called the verdict “remarkable.”

“Here was a guy protected by the community, supported by the community, and the case against him was from a young girl,” Professor Heilman said. Among the things it demonstrates, he said, is that “the district attorney should have started this kind of thing sooner.”

The verdict against Mr. Weberman was a deeply emotional moment for the young woman, who is now 18, and her family, according to her mother, who spoke in a telephone interview several hours after the verdict.

“I cried and cried, and couldn’t stop crying,” said the woman, whose name is being withheld by The New York Times to shield the identity of her daughter. “I couldn’t stop crying that justice came out.”

Mr. Weberman did not show emotion as the word “guilty” was read out, 59 times, in the 20th floor courtroom. He looked briefly at members of his family, who held on to each other as the verdict was read, and then was led into custody.

One of Mr. Weberman’s lawyers, George Farkas, said he would appeal.

“We firmly believe that this jury got an unfairly sanitized version of the facts, and as a result the truth did not come out,” he said. “The struggle to clear an innocent man will continue in full force.”

Prosecutors told reporters after the verdict that other women had come forward to assert that they had been abused by Mr. Weberman, including one who had come forward during the trial. Mr. Hynes said those women were unwilling or unable to testify, leaving his office with just one prosecutable case.

Mr. Hynes said he was hopeful that the victim’s “great courage” in testifying would encourage other women who have been abused, particularly in ultra-Orthodox communities, to come forward.

Prosecution of sexual abuse allegations in the ultra-Orthodox community has been hampered in the past by the intimidation of witnesses. In this case, Mr. Hynes’s office brought charges against four men for allegedly trying to interfere with the case, through bribery and threats. Then, during the trial, four other men were charged with criminal contempt in the second degree for taking cellphone pictures of the victim, in violation of court rules. And although supporters of accused abusers often dominated the galleries at previous trials of ultra-Orthodox Jewish men, on many days at this trial, supporters of the accuser and advocates for abuse victims were in the majority.

Rabbi Yosef Blau, a victims’ advocate and the spiritual supervisor of Yeshiva University, said he hoped that the Satmar community would now be forced to change how it dealt with troubled young people, who, like this young victim, had been sent to counselors without training or accountability, instead of licensed professionals.

“It’s a system which allowed this abuse to take place,” he said. “It involves no scrutiny, no controls, and is a terrible way of dealing with children who have issues, whatever those issues might be.”

But Pearl Engleman of Williamsburg, who became a victims’ advocate after her son said that he had been molested in the Satmar school system, said it would take more than this case to transform her community. Hundreds turned up for a fund-raiser in Mr. Weberman’s support this year, and even with a guilty verdict, she said, she does not expect many to change their minds.

“There are people who are still rooting for him,” she said. “They just can’t wrap their heads around a Jew sitting in jail for that much time.”